I have never seen this before, but this has happened to different mushrooms in the past few months. So basically between my pistol shrimp and cucumber I have a constantly moving sand bed. A month ago a red one got covered and I did not notice in time. When I lifted the rock above the sand, one of the lower red mushrooms looked like it had almost completely dissolved. This morning one of my Saint Thomas mushrooms, the entire right side of it had done the same. I grabbed some of the pieces and I will try to frag it. In the past when I had a mushroom not get enough light it just lost it's color. Do I have a predator or is this just the mushroom being smothered with sand?